As one of conventional housings for semiconductor devices each including an insert nut, there has been a housing in which a nut for insert and an electrode for insert are incorporated in a mold. In a molding method using this technique, if there is even a small gap between the electrode and the nut at the time of molding, resin enters the gap, so that wraparound of the resin occurs after the molding. The wraparound of the resin between the electrode and the nut causes resin creep at the time of bolt tightening, so that there is a concern that a decrease in axial force during use or immediately after the tightening is caused. There is a possibility that the decrease in axial force largely impairs assumed quality, and prevention of the resin wraparound is a very important factor on molding.
Therefore, when the mold, the nut, and the housing at the time of molding are designed, dimensions and tolerances for eliminating the gap between the electrode and the nut need to be set. Since performance of respective members, variation in molding conditions and the like need to be considered, controlling the wraparound only by dimensional design is at a very high difficulty level, and for this, experience and technique are required.
Moreover, when the insert nut is made of a magnetic body such as iron and the like, there has been known a method in which a magnet is provided on a movable mold side, and the insert nut is attracted to the magnet, by which opposed end surfaces of a head portion of a pin member and the insert nut are caused to closely adhere to thereby prevent inflow of melted resin between both (Patent Document 1). Moreover, there has been known a method for obtaining a similar effect by using an electromagnet in place of this magnet (Patent Document 2). Moreover, there has been known a method for providing a magnetic force for a pin for guide or the like in place of a mold (Patent Document 3). However, in the case where a permanent magnet is brought into contact with the mold or the pin for guide to attract the insert nut, there is a concern that the magnetic force is lost due to a high temperature during the molding, and that constant quality cannot be maintained. Moreover, in the electromagnetization as well, necessity for securing a space due to a power supply additionally provided, and deterioration in cost of electricity are supposed, so that the current state is that the magnetization cannot be easily utilized or introduced.